Compatible low crystalline silica spacers

ABSTRACT

The present disclosure relates to spacer fluids for use in subterranean operations and, more particularly, in certain embodiments, to spacer fluids that include a spacer additive comprising a solid scouring material and a biopolymer gum while being essential free of clay. An example method may comprise spacer fluid comprise water and a spacer additive. The spacer additive may comprise a solid scouring material and a biopolymer gum, wherein the solid scouring material comprises crystalline silica in an amount of about 5 wt. % or less, and wherein the spacer fluid is essentially free of clay. The example method may further comprise and introducing the spacer fluid into a wellbore to displace at least a portion of a first fluid in the wellbore.

BACKGROUND

Spacer fluids are often used in subterranean operations to facilitateimproved displacement efficiency when introducing new fluids into a wellbore. For example, a spacer fluid can be used to displace a fluid in awell bore before introduction of another fluid. When used for drillingfluid displacement, spacer fluids can enhance solids removal as well asseparate the drilling fluid from a physically incompatible fluid. Forinstance, in primary cementing operations, the spacer fluid may beplaced into the well bore to separate the cement composition from thedrilling fluid. Spacer fluids may also be placed between differentdrilling fluids during drilling change-outs or between a drilling fluidand completion brine. Spacer fluids typically do not consolidate in thatthe spacer fluids typically do not develop significant gel orcompressive strength.

The spacer fluid can have certain characteristics to improve itseffectiveness. For example, the spacer fluid may be compatible with thedisplaced fluid and the cement composition. This compatibility may alsobe present at downhole temperatures and pressures. In some instances,spacer fluids may be used to displace oil-based drilling fluids, oftenreferred to as “oil-based muds,” from a wellbore. Oil-based drillingfluids are typically an invert emulsion that includes an aqueousinternal phase and an oil external phase. However, certain spacer fluidsmay exhibit negative interactions when contact and mixing occurs in thewellbore with the oil-based drilling fluids. This negative interactionmay be referred to as “incompatibility” and may be observed as asignificant increase in viscosity greater than either the viscosity ofthe spacer fluid or the oil-based drilling fluid.

BRIEF DESCRIPTION OF THE DRAWINGS

These drawings illustrate certain aspects of some of the embodiments ofthe present disclosure and should not be used to limit or define thepresent disclosure.

FIG. 1 is a schematic illustration of an example system for thepreparation and delivery of a spacer fluid to a wellbore.

FIG. 2 is a schematic illustration of an example in which a spacer fluidis used between a cement composition and a drilling fluid.

FIG. 3 is a schematic illustration of the embodiment of FIG. 2 showingdisplacement of the drilling fluid.

DETAILED DESCRIPTION

The present disclosure relates to spacer fluids for use in subterraneanoperations and, more particularly, in certain embodiments, to spacerfluids that include a spacer additive comprising a solid scouringmaterial and a biopolymer gum while being essential free of clay. Byusing the biopolymer gum instead of clay for viscosity, the spacerfluids may have improved compatibility with displaced fluids, such asoil-based drilling fluids. In addition, the spacer fluids may exhibitimproved resistance to gelation upon contact with oil-based drillingfluids in the well bore, resulting in improved recovery of the oil-baseddrilling fluids and reduced equivalent circulating density. The spacerfluids may also include a solid surfactant composite, for example, thatshould also improve compatibility of the spacer fluid. The solidscouring material used in the spacer fluids may also be considered lowcrystalline silica (i.e., about 5 wt. % or less). By using solidsscouring materials that are low crystalline silica, exposure of personalcrystalline silica may be reduced, thus reducing or potentially limitinghealth hazards from inhalation of silica particles. In addition to thesolid scouring material, biopolymer gum, and solid surfactant, thespacer fluids may further include defoaming agents and weighting agentsas desired for a particular application.

Embodiments may include preparing a spacer dry blend that includes aspacer additive and a solid surfactant composite, wherein the spaceradditive comprises a solid scouring material and a biopolymer gum. Thespacer dry blend may further include optional additives, including,defoaming agents and weighting agents. The spacer dry blend may beprepared at any suitable location. By way of example, the spacer dryblend may be prepared at the well site or at a remote location from thewell site, such as a cement bulk plant. At the well site, the spacer dryblend may be combined with water, and the resulting spacer fluid maythen be pumped into the wellbore. In other embodiments, one or more ofspacer fluid components may be individually combined with the water atthe well site to form the spacer fluid.

Embodiments of the spacer fluids may include spacer additive thatincludes a solid scouring material, for example, to scrub and facilitateremoval of solid filter cake on wellbore surfaces. In some embodiments,suitable solid scouring materials may have a Mohs hardness of about 6 ofgreater. In some embodiments, suitable solid scouring materials may havea high angularity such that the solid scouring material has sharp and/orjagged corners. By having sharp and/or jagged corners, the solidscouring material may have improved scouring with higher impactpressures. Angularity and roundness are both terms that can be used todescribe the shape of the corners on a particle. The higher theangularity of a particle (e.g., angular particle), the lower theroundness of that particle. Similarly, the higher the roundness of aparticle, the lower the angularity of that particle. As will beappreciated by one of skill in the art, and with the help of thisdisclosure, examples of suitable solid scouring materials may have highangularity. In some embodiments, suitable solid scouring materials haveroundness of less than about 0.6 and a sphericity less than about 0.6.Roundness generally refers to the sharpness of the corners and edges ofa grain/particle and it may be defined as the ratio of the averageradius of curvature of the corners to the radius of the largestinscribed circle. Since can be quite time consuming to measureroundness, the common method of estimating roundness is to visuallycompare grains of unknown roundness with standard images of grains ofknown roundness. Sphericity generally measures the degree to which aparticle approaches a spherical shape, and it may be defined as theratio between the diameter of a sphere with the same volume as theparticle and the diameter of the circumscribed sphere. The sphericity ofa particle is usually determined by measuring the three lineardimensions of the particle: longest diameter, intermediate diameter andshortest diameter.

In addition, the solid scouring material may be considered lowcrystalline silica, in that the solid scouring material may containreduced amounts of crystalline silica (i.e., about 5 wt. % or less). Forexample, the solid scouring material may contain crystalline silica inan amount of about 5 wt. % or less, about 3 wt. % or less, or about 1wt. % or less. In some embodiments, the solid scouring material may befree and/or essentially free of crystalline silica.

Examples of suitable solid scouring materials may include, but are notlimited to, pumice, perlite, other volcanic glasses, fumed silica, andfly ash, among others. In embodiments, the solid scouring material mayhave a specific gravity of about 2.5 or less. In some embodiments, thesolid scouring material may include pumice. Generally, pumice is avolcanic rock that can exhibit cementitious properties in that it mayset and harden in the presence of hydrated lime and water. The pumicemay also be ground. Generally, the pumice may have any particle sizedistribution as desired for a particular application. In certainembodiments, the pumice may have a mean particle size of about 1 micronto about 200 microns as defined by ASTM methods. The mean particle sizecorresponds to d50 values as measured by particle size analyzers such asthose manufactured by Malvern Instruments, Worcestershire, UnitedKingdom. In specific embodiments, the pumice may have a mean particlesize of from about 1 micron to about 200 microns, from about 5 micronsto about 100 microns, or from about 10 microns to about 25 microns. Thesolid scouring material may be present in the spacer additive in anysuitable amount, including, but not limited to, an amount of about 50wt. % to about 99.9 wt. % based on a total weight of the spaceradditive. In specific embodiments, the solid scouring material may bepresent in an amount of about 90 wt. % to about 99 wt. % or from about95 wt. % to about 98 wt. % based on a total weight of the spaceradditive. In a specific example, the solid scouring material may bepresent in the spacer additive in an amount of about 97.6 wt. % based ona total weight of the spacer additive. One of ordinary skill in the art,with the benefit of this disclosure, should be able to select anappropriate particle size and concentration for the solid scouringmaterial.

Embodiments of the spacer fluids may include a spacer additive thatincludes a biopolymer gum. Examples of suitable biopolymer gums mayinclude, but are not limited to, xanthan gum, diutan gum, welan gum,scleroglucan gum, and combinations thereof. The biopolymer gum may bepresent in the spacer additive in any suitable amount, including, butnot limited to, an amount of about 0.1 wt. % to about 10 wt. % based ona total weight of the spacer additive. In specific embodiments, thesolid scouring material may be present in an amount of about 1 wt. % toabout 5 wt. % or from about 2 wt. % to about 3 wt. % based on a totalweight of the spacer additive. In a specific example, the biopolymer gummay be present in the spacer additive in an amount of about 97.6 wt. %based on a total weight of the spacer additive. One of ordinary skill inthe art, with the benefit of this disclosure, should be able to selectan appropriate concentration for the biopolymer.

The rheology and amount of solid scouring material and biopolymer gum inthe spacer dry blend containing scouring agent, biopolymer gum, solidsurfactant composite, defoaming agent, and/or weighting agent may bemodified as desired to obtain a spacer fluid with desired properties.For example, reducing the weight percent of the biopolymer gum in thespacer dry blend should reduce the shear stress produced by the spacerfluid at a given shear rate per unit mass of spacer additive in thespacer dry blend. At low amounts such as 0.1 wt. % biopolymer gum in thespacer additive achieving needed rheology in higher density spacerfluids may be hindered. If weight percent of the biopolymer gum in thespacer additive is increased to an elevated amount such as 10 wt. % orhigher, the amount of solid scouring material may be reduced to such anextent that it becomes ineffective at scrubbing mud filter cake from thewellbore. In some embodiments, the spacer additive may have a biopolymergum to solid scouring material weight ratio of about 0.5:99.5 to about10:90 or about 1:99 to about 5:95 or from about 2:98 to about 3:97. Insome embodiments, the biopolymer to solid scouring material weight ratiomay be about 2.4 biopolymer gum to about 97.6 solid scouring material.

The spacer additive may be included in the spacer dry blend in anysuitable amount. In some embodiments, the spacer additive including thesolid scouring material and the biopolymer gum may be included in thespacer dry blend in an amount of about 20 wt. % to about 100 wt. % basedon a total weight of the spacer dry blend. In specific embodiments, thespacer dry blend may be present in an amount of about 20 wt. % to about50 wt. %, about 60 wt. % to about 99 wt. %, about 80 wt. % to about 99wt. %, or about 90 wt. % to about 100 wt. % based on a total weight ofthe spacer dry blend.

Embodiments of the spacer fluids may include a solid surfactantcomposite, which may include a surfactant and a solid carrier.Optionally, the solid surfactant composite may include a dispersant, adefoaming agent, or a combination thereof. The solid surfactantcomposite may have a wide variety of shapes and sizes of individualparticles suitable for use in well applications. By way of example,individual particles of the solid surfactant composite may havewell-defined physical as well as irregular geometries, including thephysical shape of platelets, shavings, fibers, flakes, ribbons, rods,strips, spheroids, hollow beads, toroids, pellets, tablets, or any otherphysical shape. Without limitation, the solid surfactant composite mayhave a mean particle size in the range of about 5 microns to about 1,500microns and, alternatively, a mean particle size in the range of about20 microns to about 500 microns. However, particle sizes outside thesedefined ranges also may be suitable for particular applications.

The solid surfactant composite may be included in the spacer dry blendin any suitable amount. In some embodiments, the solid surfactantcomposite may be included in the spacer dry blend in an amount of about0.1 wt. % to about 10 wt. % based on a total weight of the spacer dryblend. In specific embodiments, the spacer dry blend may be present inan amount of about 1 wt. % to about 10 wt. %, about 1 wt. % to about 5wt. %, or about 2 wt. % to about 5 wt. % based on a total weight of thespacer dry blend.

Any of a variety of surfactants may be included in the solid surfactantcomposite that may be capable of wetting well surfaces (e.g., water- oroil-wetting), such as the wellbore wall and casing surface. The functionthat a particular surfactant may perform depends on a variety offactors. These factors may include, but are not limited to, the choiceof the hydrophobic and hydrophilic portions and the relative amountsthereof and the presence of any cationic, ionic, non-ionic, amphoteric,or Zwitterionic groups. In some embodiments, both a water-wettingsurfactant and an oil-wetting surfactant may be included in the solidsurfactant composite. The wetting surfactant may be included in thesolid surfactant composite in an amount, without limitation, of fromabout 5 wt. % to about 99.9 wt. % based on a total weight of the solidsurfactant composite. By way of example, the wetting surfactant may beincluded in an amount of from about 5 wt. %, about 10 wt. %, about 20wt. %, about 30 wt. %, about 40 wt. %, about 50 wt. %, about 60 wt. %,about 70 wt. %, about 80 wt. %, about 90 wt. %, or about 99.9 wt. %based on a total weight of the solid surfactant composite. Examples ofsuitable wetting surfactants may include alcohol ethoxylates, alcoholethoxysulfates, alkyl phenol ethoxylates (e.g., nonyl phenolethoxylates), glycol ethers, and combinations thereof. Certain of thewetting surfactants may be used as water-soluble salts. For example, thewetting surfactants may be selected from alkali metal, alkaline earthmetal, ammonium, and alkanolammonium salts of alcohol ethoxylates,alcohol ethoxysulfates, and alkyl phenol ethoxylates. One of ordinaryskill in the art, with the benefit of this disclosure, should be able toselect an appropriate wetting surfactant and concentration thereof for aparticular application.

As previously described, the wetting surfactant may be disposed on asolid carrier. Without limitation, the solid carrier may include any ofa variety of solid materials, such as diatomaceous earth, amorphoussilica, starch, calcium silicate, and combinations thereof. The solidcarrier may be included in the solid surfactant composite in an amount,without limitation, of from about 0.1 wt. % to about 95 wt. % based on atotal weight of the solid surfactant composite. By way of example, thesolid carrier may be included in an amount of from about 0.1 wt. %,about 10 wt. %, about 20 wt. %, about 30 wt. %, about 40 wt. %, about 50wt. %, about 60 wt. %, about 70 wt. %, about 80 wt. %, about 90 wt. %,or about 95 wt. % based on a total weight of the solid surfactantcomposite. One of ordinary skill in the art, with the benefit of thisdisclosure, should be able to select an appropriate solid carrier andconcentration thereof for a particular application.

Optionally, the solid surfactant composite may include a dispersant.Without limitation, suitable dispersants may include any of a variety ofcommonly used cement dispersants, such as sulfonated dispersants;sulfonated polymer dispersants; naphthalene sulfonates; melaminesulfonates; sulfonated melamine formaldehyde condensate; sulfonatednaphthalene formaldehyde condensate; sulfonate acetone formaldehydecondensate; ethoxylated polyacrylates; or combinations thereof. Oneexample of a suitable dispersant may include a naphthalene sulfonatecondensed with from about 4 moles to about 8 moles and, alternatively,about 6 moles of formaldehyde. The dispersant may be included in thesolid surfactant composite in an amount, without limitation, of fromabout 10 wt. % to about 90 wt. % based on a total weight of the solidsurfactant composite. By way of example, the dispersant may be includedin an amount of from about 10 wt. %, about 20 wt. %, about 30 wt. %,about 40 wt. %, about 50 wt. %, about 60 wt. %, about 70 wt. %, about 80wt. %, or about 90 wt. % based on a total weight of the solid surfactantcomposite. One of ordinary skill in the art, with the benefit of thisdisclosure, should be able to select an appropriate dispersant andconcentration thereof for a particular application.

Optionally, the solid surfactant composite may include a defoamingagent. The defoaming agent may be include in the solid surfactantcomposite in addition to, or separate from, the dispersant. Suitabledefoaming agents may include compounds used in well operations toprevent a well treatment fluid from foaming during mixing and pumping.Without limitation, suitable defoaming agents may include polyolcompositions, siloxanes such as polydimethyl siloxane, acetylenic diols,and combinations thereof. The defoaming agent may be included in thesolid surfactant composite in addition to, or separate from, thedispersant. The defoaming agent may be included in the solid surfactantcomposite in an amount, without limitation, of from about 0.1 wt. % toabout 20 wt. % based on a total weight of the solid surfactantcomposite. By way of example, the defoaming agent may be included in anamount of from about 0.1 wt. %, about 5 wt. %, about 10 wt. %, about 15wt. %, or about 20 wt. % based on a total weight of the solid surfactantcomposite. One of ordinary skill in the art, with the benefit of thisdisclosure, should be able to select an appropriate defoaming agent andconcentration thereof for a particular application.

Without limitation, a solid surfactant composite may include an alcoholethoxylate, a solid carrier including amorphous silica, a dispersant,and a defoaming agent. By way of example, the solid surfactant compositemay include a C₈ to C₁₂ alcohol substituted with about 4 moles to about8 moles of ethylene oxide, amorphous silica, a sulfonated naphthaleneformaldehyde condensate, and a siloxane. By way of further example, thesolid surfactant composite may include isodecyl alcohol substituted with6 moles of ethylene oxide, amorphous silica, naphthalene sulfonatecondensed with 6 moles of formaldehyde, and a polydimethyl siloxane.

Without limitation, a solid surfactant composite may include an alcoholethoxylate, a solid carrier, a dispersant, and a defoaming agent. By wayof example, the solid surfactant composite may include a C₁₂ to C₁₄alcohol substituted with about 10 moles to about 14 moles of ethyleneoxide, amorphous silica, diatomaceous earth, a sulfonated naphthaleneformaldehyde condensate, and a siloxane. By way of further example, thesolid surfactant composite may include isotridecyl alcohol substitutedwith 12 moles ethylene oxide, amorphous silica, diatomaceous earth,naphthalene sulfonate condensed with 6 moles of formaldehyde, and apolydimethyl siloxane.

The solid surfactant composite may be prepared by any suitabletechnique. By way of example, the components (e.g., wetting surfactant,solid carrier, dispersant, and/or defoaming agent) may be combined toform a mixture. This mixture may then be dried, such as by spray drying,to form a substantially dry solid product. Other suitable techniques forpreparation of the solid surfactant composite may also be used as shouldbe apparent to one of ordinary skill in the art.

A wide variety of additional additives may be included in the spacer dryblend as deemed appropriate by one skilled in the art, with the benefitof this disclosure. Examples of such additives include but are notlimited to: weighting agents (e.g., barite), defoaming agents. Weightingagents may be included in the spacer dry blend, for example, to providethe spacer fluid with a desired density. Examples of suitable weightingagents include, for example, materials having a specific gravity of 2.5or greater, such as barite, manganese tetraoxide, iron oxide, calciumcarbonate, or iron carbonate. Weighting agents may be included in anysuitable amount, including, but not limited to, from about 1 wt. % toabout 99 wt. %, about 50 wt. % to about 99 wt. %, or about 75 wt. % toabout 99 wt. % based on a total weight of the spacer dry blend.Defoaming agents may be included in the spacer dry blend, for example,to reduce undesirable foaming in the spacer fluid upon mixing andinstruction into the wellbore. Examples of suitable defoaming agents mayinclude, but are not limited to, polyol compositions, siloxanes such aspolydimethyl siloxane, acetylenic diols, ethoxylated alcohols,propoxylated alcohols, fatty alcohol ethoxylates, internal olefins andcombinations thereof. Defoaming agents may be included in any suitableamount, including, but not limited to, from about 0.01 wt. % to about 10wt. %, about 0.05 wt. % to about 5 wt. %, or about 0.05 wt. % to about 1wt. % based on a total weight of the spacer dry blend. A person havingordinary skill in the art, with the benefit of this disclosure, shouldreadily be able to determine the type and amount of additive useful fora particular application and desired result. While these additives aredescribed as being included in the spacer dry blend, it is alsocontemplated that one or more of these additives may be added directlyto the water, which may occur before, during, or after addition of thespacer dry blend to the water.

As previously described, the spacer dry blend may be combined with waterto form a spacer fluid, which may then be introduced into the wellbore.The water used in an embodiment of the spacer fluids may include, forexample, freshwater, saltwater (e.g., water containing one or more saltsdissolved therein), brines, seawater, or any combination thereof.Generally, the water may be from any source, provided that the waterdoes not contain an excess of compounds that may undesirably affectother components in the spacer fluid. The water is included in an amountsufficient to form a pumpable spacer fluid. In some embodiments, thewater may be included in the spacer fluids in an amount in the range offrom about 15 wt. % to about 95 wt. % based on a total weight of thespacer fluid. In other embodiments, the water may be included in thespacer fluids in an amount in the range of from about 25 wt. % to about85 wt. % or about 50 wt. % to about 75 wt. % based on a total weight ofthe spacer fluid. The spacer dry blend may be included in the spacerfluid in any suitable amount, including about 5 wt. % to about 50 wt. %,about 10 wt. % to about 60 wt. %, or about 20 wt. % to about 50 wt. %based on a total weight of the spacer fluid. One of ordinary skill inthe art, with the benefit of this disclosure, should recognize theappropriate amount of water and spacer dry blend to include for a chosenapplication.

In addition, the spacer fluids and/or spacer dry blends may beconsidered low crystalline silica, in that the spacer fluids and/or dryspacer fluids may contain reduced amounts of crystalline silica, notincluding any potential weighting agent (e.g., barite) that may beincluded. For example, the spacer fluids and/or spacer dry blends maycontain crystalline silica in an amount of about 5% or less, about 3% orless, or about 1% or less by weight. In some embodiments, the spacerfluids and/or spacer dry blends may be free and/or essentially free ofcrystalline silica.

In addition, embodiments of the spacer fluids and/or spacer dry blendsmay be essentially free of clay in that they may contain no clay, or, tothe extent that clay may be present, the clay is present in an amount ofno more than 2 wt. %. In some embodiments, the spacer fluids may containno clay, or, to the extent that clay may be present, the clay is presentin an amount of no more than 1 wt. %, 0.5 wt. %, 0.1 wt. %, or less. Anumber of different clays are commonly included in spacer fluids and/orspacer dry blends, including, but not limited to, montmorillonite clays,attapulgite clays, and sepiolite clays. In contrast to conventionalspacers fluids that utilize clay for viscosity, the spacer fluidscomprising the spacer additive may use the biopolymer gum for viscosity.When clays are intercalated the platelets are stacked in layers withions between the layers. As the clays exfoliate surfactants and ionicfluids with the mud often interact unpredictably with ionically chargedplatelets. This can result in gelation as well as lack of appropriateviscous properties. By reducing or potentially even eliminating clayfrom the spacer fluids, the spacer fluid may have increasedcompatibility with displaced or adjacent fluids.

The spacer fluids generally should have a density suitable for aparticular application as desired by those of ordinary skill in the art,with the benefit of this disclosure. In some embodiments, the spacerfluids may have a density in the range of from about 4 pounds per gallon(“lb/gal”) (480 kg/m³) to about 24 lg/gal (2900 kg/m³). In otherembodiments, the spacer fluids may have a density in the range of about4 lb/gal (480 kg/m³) to about 17 lb/gal (2040 kg/m³). In yet otherembodiments, the spacer fluids may have a density in the range of about8 lg/gal (960 kg/m³) to about 13 lb/gal (1600 kg/m³). Embodiments of thespacer fluids may be foamed or unfoamed or include other means to reducetheir densities known in the art, such as lightweight additives. Thoseof ordinary skill in the art, with the benefit of this disclosure, willrecognize the appropriate density for a particular application.

Suitable spacer fluids may be prepared in accordance with any suitabletechnique. Without limitation, the desired quantity of water may beintroduced into a mixer (e.g., a cement blender) followed by the spacerdry blend. Additional liquid additives and/or dry additives, if any, maybe added to the water as desired prior to, or after, combination withthe dry blend. This mixture may be agitated for a sufficient period oftime to form a pumpable slurry. By way of example, pumps may be used fordelivery of this pumpable slurry into the wellbore. As will beappreciated, the spacer fluid and/or the spacer dry blend may beprepared at the well site or prepared offsite and then transported tothe well site. If prepared offsite, the spacer dry blend and/or spacerfluid may be transported to the well site using any suitable mode oftransportation, including, without limitation, a truck, railcar, barge,or the like. Alternatively, the spacer fluid and/or spacer dry blend maybe formulated at the well site, for example, where the components of thespacer fluid and/or spacer dry blend may be delivered from a transport(e.g., a vehicle or pipeline) and then mixed prior to placementdownhole. As will be appreciated by those of ordinary skill in the art,with the benefit of this disclosure, other suitable techniques forpreparing the spacer fluids may be used in accordance with embodiments.

With limitation, the spacer fluid (as described herein) may be used fordisplacing a first fluid from a wellbore, the wellbore penetrating asubterranean formation. The method may further include introducing thespacer fluid into the wellbore to displace at least a portion of thefirst fluid from the wellbore. Without limitation, the spacer fluid maydisplace the first fluid from a wellbore annulus, such as the annulusbetween a pipe string and the subterranean formation or between the pipestring and a larger conduit. Non-limiting examples of the first fluiddisplaced by the spacer fluid may include a drilling fluid. By way ofexample, the spacer fluid may be used to displace the drilling fluidfrom the wellbore. In addition to displacement of the drilling fluidfrom the wellbore, the spacer fluid may also remove the drilling fluidfrom the walls of the wellbore and/or piper string. Additional steps inthe method may include, without limitation, introducing a pipe stringinto the wellbore, introducing a cement composition into the wellborewith the spacer fluid separating the cement composition and the firstfluid.

As described herein, the spacer fluid may prevent the cement compositionfrom contacting the first fluid, such as a drilling fluid. The spacerfluid may also remove the drilling fluid, dehydrated/gelled drillingfluid, and/or filter cake solids from the wellbore in advance of thecement composition. Removal of these compositions from the wellbore mayenhance bonding of the cement composition to surfaces in the wellbore.

The displaced drilling fluid may include, for example, any number offluids, such as solid suspensions, mixtures, and emulsions. Anon-limiting example of a suitable drilling fluid may include anoil-based drilling fluid. An example of a suitable oil-based drillingfluid includes an invert emulsion. Without limitation, the oil-baseddrilling fluid may include an oleaginous fluid. Examples of suitableoleaginous fluids that may be included in the oil-based drilling fluidsinclude, but are not limited to, α-olefins, internal olefins, alkanes,aromatic solvents, cycloalkanes, liquefied petroleum gas, kerosene,diesel oils, crude oils, gas oils, fuel oils, paraffin oils, mineraloils, low-toxicity mineral oils, olefins, esters, amides, synthetic oils(e.g., polyolefins), polydiorganosiloxanes, siloxanes, organosiloxanes,ethers, dialkylcarbonates, hydrocarbons, and combinations thereof.

The cement composition introduced into the wellbore may includehydraulic cement and water. A variety of hydraulic cements may beutilized in accordance with the present embodiments, including, but notlimited to, those including calcium, aluminum, silicon, oxygen, iron,and/or sulfur, which set and harden by reaction with water. Suitablehydraulic cements include, but are not limited to, Portland cements,pozzolana cements, gypsum cements, high alumina content cements, slagcements, silica cements, and combinations thereof. In certainembodiments, the hydraulic cement may include a Portland cement. In someembodiments, the Portland cements may include cements classified asClasses A, C, H, or G cements according to American Petroleum Institute,API Specification for Materials and Testing for Well Cements, APISpecification 10, Fifth Ed., Jul. 1, 1990. In addition, in someembodiments, the hydraulic cement may include cements classified as ASTMType I, II, or III.

Without limitation, methods of using the spacer fluids described hereinin well cementing will now be described in more detail with reference toFIGS. 1-3. Any of the embodiments of a spacer fluid described herein mayapply in the context of FIGS. 1-3. FIG. 1 illustrates an example system100 that may be used for preparation and delivery of a spacer fluiddownhole. It should be noted that while FIG. 1 generally depicts aland-based operation, those skilled in the art will readily recognizethat the principles described herein are equally applicable to subseaoperations that employ floating or sea-based platforms and rigs, withoutdeparting from the scope of the disclosure. As illustrated on FIG. 1,the system 100 may include a vessel 105 and a pump 110. The pump 110 maybe positioned downstream of the vessel 105 and may be fluidly coupled toa tubular 115 that is in fluid communication with the wellbore 120. Thetubular 115 may be configured to circulate or otherwise deliver thespacer fluid to the wellbore 120. The tubular 115 may be comprised, forexample, of one or more different pipes that extend into the wellbore120. The pump 110 may be, for example, one or more high pressure orlow-pressure pumps, which may be depend on, without limitation, theviscosity and density of the spacer fluid. Without limitation, the pump110 may draw the spacer fluid from the vessel 105, elevate the spacerfluid to an appropriate pressure, and then introduce the spacer fluid tothe tubular 115 for delivery downhole. Without limitation, the vessel105 and pump 110 may be disposed on one or more cement trucks, forexample. While not illustrated, system 100 may further include arecirculating mixer, a batch mixer and/or a jet mixer, which may be usedfor example, in preparation and/or storage of the spacer fluid.Non-limiting additional components that may be present include, but arenot limited to, supply hoppers, valves, condensers, adapters, joints,gauges, sensors, compressors, pressure controllers, pressure sensors,flow rate controllers, flow rate sensors, temperature sensors, and thelike.

FIG. 2 depicts one or more subterranean formations 200 penetrated bywellbore 120 with drilling fluid 205 disposed therein. The drillingfluid 205 may include the example drilling fluids disclosed herein aswell as other suitable drilling fluids that will be readily apparent tothose of ordinary skill in the art. While the wellbore 120 is shownextending generally vertically into the one or more subterraneanformations 200, the principles described herein are also applicable towellbores that extend at an angle through the one or more subterraneanformations 200, such as horizontal and slanted wellbores. Asillustrated, the wellbore 120 includes walls 210. Without limitation, asurface casing 215 may be cemented to the walls 210 of the wellbore 120by cement sheath 220. Without limitation, one or more additional pipestrings (e.g., intermediate casing, production casing, liners, etc.),shown here as casing 225 may also be disposed in the wellbore 120. Asillustrated, there is a wellbore annulus 230 formed between the casing225 and the walls 210 of the wellbore 120 (and/or a larger conduit suchas the surface casing 215). While not shown, one or more centralizersmay be attached to the casing 225, for example, to centralize the casing225 in the wellbore 120 prior to and during the cementing operation.

As illustrated, a cement composition 235 may be introduced into thewellbore 120. For example, the cement composition 235 may be pumped downthe interior of the casing 225. A pump (e.g. pump 110 on FIG. 1) may beused for delivery of the cement composition 235 into the wellbore 120.It may be desired to circulate the cement composition 235 in thewellbore 120 until it is in the wellbore annulus 230. The cementcomposition 235 may include the example cement compositions disclosedherein as well as other suitable cement compositions that will bereadily apparent to those of ordinary skill in the art. While notillustrated, other techniques may also be utilized for introduction ofthe cement composition 235. By way of example, reverse circulationtechniques may be used that include introducing the cement composition235 into the wellbore 120 by way of the wellbore annulus 230 instead ofthrough the casing 225.

Without limitation, the spacer fluid 240 may be used to separate thedrilling fluid 205 from the cement composition 235. The previousdescription with reference to FIG. 1 for preparation of a spacer fluidmay be used for delivery of the spacer fluid 240 into the wellbore 120.Moreover, a pump (e.g., pump 110 on FIG. 1) may also be used fordelivery of the spacer fluid 240 into the wellbore 120. The spacer fluid240 may be used with the cement composition 235 for displacement of thedrilling fluid 205 from the wellbore 120 as well as preparing thewellbore 120 for the cement composition 235. By way of example, thespacer fluid 240 may function, inter alia, to remove the drilling fluid205, drilling fluid 205 that is dehydrated/gelled, and/or filter cakesolids from the wellbore 120 in advance of the cement composition 235.While not shown, one or more plugs or other suitable devices may be usedto physically separate the drilling fluid 205 from the spacer fluid 240and/or the spacer fluid 240 from the cement composition 235.

Referring now to FIG. 3, the drilling fluid 205 has been displaced fromthe wellbore annulus 230. As illustrated, the spacer fluid 240 and thecement composition 235 may be allowed to flow down the interior of thecasing 225 through the bottom of the casing 225 (e.g., casing shoe 300)and up around the casing 225 into the wellbore annulus 230, thusdisplacing the drilling fluid 205. At least a portion of the displaceddrilling fluid 205 may exit the wellbore annulus 230 via a flow line 125and be deposited, for example, in one or more retention pits 130 (e.g.,a mud pit), as shown in FIG. 1. Turning back to FIG. 3, the cementcomposition 235 may continue to be circulated until it has reached adesired location in the wellbore annulus 230. The spacer fluid 240 (or aportion thereof) and/or the cement composition 235 may be left in thewellbore annulus 230. As illustrated, the spacer fluid 240 may bedisposed in the wellbore annulus 230 above or on top of the cementcomposition 235. The cement composition 235 may set in the wellboreannulus 230 to form an annular sheath of hardened, substantiallyimpermeable material (i.e., a cement sheath) that may support andposition the casing 225 in the wellbore 120.

Accordingly, this disclosure describes spacer fluids that include aspacer additive comprising a solid scouring material and a biopolymergum while being essential free of clay. The systems and methods mayfurther be characterized by one or more of the following statements:

Statement 1. An example method may include spacer fluid include waterand a spacer additive. The spacer additive may include a solid scouringmaterial and a biopolymer gum, wherein the solid scouring materialincludes crystalline silica in an amount of about 5 wt. % or less, andwherein the spacer fluid is essentially free of clay. The example methodmay further include and introducing the spacer fluid into a wellbore todisplace at least a portion of a first fluid in the wellbore.

Statement 2. The method of statement 1, further including combining atleast a spacer dry blend and water to form the spacer fluid, wherein thespacer dry blend includes the solid scouring material and thebiopolymer.

Statement 3. The method of statement 1 or 2, wherein the solid scouringmaterial has a specific gravity of less than 2.5, and wherein the spacerfluid is free of crystalline silica or includes crystalline silica in anamount of about 1 wt. % or less, not including any components having aspecific gravity greater than 2.5.

Statement 4. The method of any preceding statement, wherein the solidscouring material has a Mohs hardness of about 6 or greater, wherein thesolid scouring material has a roundness of about 0.6 or less, andwherein the solid scouring material has a sphericity of about 0.6 orless.

Statement 5. The method of any preceding statement, wherein the solidscouring material includes at least one material selected from the groupconsisting of pumice, perlite, other volcanic glasses, fumed silica, flyash, and combinations thereof, and wherein the biopolymer gum includesat least one gum selected from the group consisting of xanthan gum,diutan gum, welan gum, scleroglucan gum, and combinations thereof.

Statement 6. The method of any preceding statement, wherein the solidscouring material includes pumice, and wherein the biopolymer gumincludes diutan gum.

Statement 7. The method of any preceding statement, wherein a weightratio of the biopolymer gum to the solid scouring material in the spaceradditive is about 10:90 to about 1:99.

Statement 8. The method of any preceding statement, wherein a weightratio of the biopolymer gum to the solid scouring material in the spaceradditive is about 3:97 to about 2:98.

Statement 9. The method of any preceding statement, wherein the spacerfluid further includes a solid surfactant composite.

Statement 10. The method of statement 9, wherein the solid surfactantcomposite has a mean particle size of about 5 microns to about 1,500microns, and wherein the solid surfactant composite includes a wettingsurfactant on a solid carrier.

Statement 11. The method of any preceding statement, wherein the spacerfluid further includes at least one additive selected from the groupconsisting of a defoaming agent, a weighting agent, and combinationsthereof.

Statement 12. The method of any preceding statement, wherein the firstfluid includes an oil-based drilling fluid.

Statement 13. The method of any preceding statement, further includingintroducing a cement composition into the wellbore behind the spacerfluid.

Statement 14. Another example may include a method for displacingwellbore fluids. The method may include providing a spacer dry blendthat includes a spacer additive, a solid surfactant composite, and aweighting agent having a specific gravity greater than 2.5, wherein thespacer additive includes pumice and diutan gum in a diutan gum to pumiceweight ratio of about 2:98 to about 3:97, and wherein the solidsurfactant composite includes a surfactant on a solid carrier. Themethod may include combining at least the spacer dry blend and water toform a spacer fluid, wherein the spacer fluid is essentially free ofclay comprising montmorillonite clay, attapulgite clay, and sepioliteclay. The method may include introducing the spacer fluid into awellbore to displace at least a portion of an oil-based drilling fluidin the wellbore.

Statement 15. The method of statement 14, further including introducinga cement composition into the wellbore behind the spacer fluid.

Statement 16. An example spacer fluid for use in displacing wellborefluids may include water and a spacer additive. The spacer additive mayinclude a solid scouring material and a biopolymer gum, wherein thesolid scouring material includes crystalline silica in an amount ofabout 2.5 wt. % or less, and wherein the spacer fluid is essentiallyfree of clay.

Statement 17. The spacer fluid of statement 16, wherein the solidscouring material has a specific gravity of less than 2.5, and whereinthe spacer fluid is free of crystalline silica or includes crystallinesilica in an amount of about 1 wt. % or less, not including anycomponents having a specific gravity greater than 2.5.

Statement 18. The spacer fluid of statement 16 or 17, wherein the solidscouring material has a Mohs hardness of about 6 or greater, wherein thesolid scouring material has a roundness of about 0.6 or less, andwherein the solid scouring material has a sphericity of about 0.6 orless.

Statement 19. The spacer fluid of any one of statements 16 to 18,wherein the solid scouring material includes pumice, and wherein thebiopolymer gum includes diutan gum.

Statement 20. The spacer fluid of any one of statements 16 to 19,wherein the spacer fluid further includes a solid surfactant composite,wherein the solid surfactant composite includes a wetting surfactant ona solid carrier.

To facilitate a better understanding of the present disclosure, thefollowing examples of certain aspects of some embodiments are given. Inno way should the following examples be read to limit, or define, thescope of the disclosure. In the following examples, concentrations aregiven in weight percent of the overall composition.

Example 1

A sample spacer fluid (Spacer 1) was prepared and evaluated for fluidcompatibility with a first oil-based mud (OBM1). Spacer 1 had a densityof 10.5 lbm/gal (1260 kg/m³) and composition provided in Table 1. SolidSurfactant Composite 1 included in Spacer 1 was a water-wettingsurfactant (C6-C10 alcohol ethoxylate sulfate ammonium salt) disposed onan amorphous silica carrier. Solid Surfactant Composite 2 was anoil-wetting surfactant (ethoxylated nonylphenol blend) disposed on anamorphous silica carrier. OBM1 was a diesel-based invert emulsiondrilling mud.

Spacer 1 was evaluated for fluid compatibility with OBM1 at 80° F. (27°C.) and 180° F. (82° C.). Spacer 1 and OBM1 were conditioned at the testtemperature for 30 minutes prior to measurement. Ratios prescribed inAPI RP 10B2 (2013) were prepared, and rheological measurements weretaken on Spacer 1, OBM1, and their mixtures using an OFITE 900 automatedviscometer having an R1-B1-F1 configuration. Dial readings from theviscometer for the fluids are shown at rotational speeds in Tables 2 and3. Rotational speeds of 60 rotations per minute (rpm) and 100 rpm are ofkey interest as they most closely approach shear rates commonlyexperienced during primary cementing. At 60 rpm and 100 rpm, none of themixtures experienced adverse gelation or a dial reading greater than 10%of that of Spacer 1, indicating good fluid rheological compatibility forSpacer 1 and OBM1.

TABLE 1 Spacer 1 Composition Material Mass, grams Pumice 111.36 Diutan2.74 Barite 210.28 Solid Surfactant Composite 1 6.85 Solid SurfactantComposite 2 6.85 Fresh Water 668.47

TABLE 2 Rheological Compatibility of Spacer 1 and OBM1 at 80° F. Ratioof OBM1 to Spacer 1 300 rpm 200 rpm 100 rpm 60 rpm 30 rpm 6 rpm 3 rpm100:0  22 17 10 8 6 2.8 2.5 95:75 25 18 11 8 6 2.8 2.5 75:25 35 24 13 107 2.6 2.1 50:50 48 38 24 18 12 5.1 3.5 25:75 47 40 31 24 17 7.6 5.5 5:95 48 42 37 31 24 14.8 11.6  0:100 46 42 38 36 32 26.6 21.8

TABLE 3 Rheological compatibility of Spacer 1 and OBM1 at 180° F. Ratioof OBM1 to 300 Spacer 1 rpm 200 rpm 100 rpm 60 rpm 30 rpm 6 rpm 3 rpm100:0  17 12 8 6 5 1.4 0.9 95:75 14 11 7 6 4 1.4 1.2 75:25 19 14 8 6 52.3 2.0 50:50 41 33 21 14 9 3.1 2.1 25:75 45 41 33 26 20 11.5 9.1  5:9546 42 39 35 30 20.9 18.4  0:100 44 41 38 35 32 27.0 22.6

Example 2

A second sample spacer fluid (Spacer 2) was prepared and evaluated forfluid compatibility with a second oil-based mud (OBM2). Spacer 2 had adensity of 11.5 lbm/gal (1380 kg/m³) and composition provided in Table4. Spacer 2 was evaluated for fluid compatibility at 80° F. (27° C.) and180° F. (82° C.) with OBM2. OBM2 was a diesel-based invert emulsiondrilling mud. Spacer 2 and OBM2 were conditioned at the test temperaturefor 30 minutes prior to measurement. Ratios prescribed in API RP 10B2(2013) were prepared, and rheological measurements were taken on Spacer2, OBM2, and their mixtures using an OFITE 900 automated viscometerhaving an R1-B1-F1 configuration. Dial readings from the viscometer forthe fluids are shown at rotational speeds in Tables 5 and 6. Rotationalspeeds of 60 rpm and 100 rpm are of key interest as they most closelyapproach shear rates commonly experienced during primary cementing. At60 rpm and 100 rpm none of the mixtures experienced adverse gelation ora dial reading greater than 10% of that of Spacer 2, indicating goodfluid rheological compatibility for Spacer 2 and OBM2.

TABLE 4 Spacer 2 Composition Material Mass, grams Pumice 69.35 Diutan1.71 Barite 356.98 Solid Surfactant Composite 1 6.85 Solid SurfactantComposite 2 6.85 Fresh Water 660.68

TABLE 5 Rheological Compatibility of Spacer 2 and OBM2 at 80° F. Ratioof OBM2 to 300 Spacer 2 rpm 200 rpm 100 rpm 60 rpm 30 rpm 6 rpm 3 rpm100:0  19 14 8 6 4 1.1 0.9 95:75 22 15 9 6 4 1.2 0.9 75:25 29 18 10 6 31.2 1.0 50:50 48 35 24 18 13 8.3 8.1 25:75 39 32 22 17 13 8.6 7.7  5:9536 30 24 21 16 9.7 7.6  0:100 32 28 23 21 19 15.4 13.5

TABLE 6 Rheological Compatibility of Spacer 2 and OBM2 at 180° F. Ratioof OBM2 to 300 Spacer 2 rpm 200 rpm 100 rpm 60 rpm 30 rpm 6 rpm 3 rpm100:0  12 9 6 3 2 1.0 0.9 95:75 13 9 5 5 2 0.6 0.5 75:25 25 12 6 4 2 0.50.4 50:50 47 38 22 15 11 8.6 8.4 25:75 33 30 25 20 15 11.2 10.5  5:95 2826 22 20 16 10.7 9.4  0:100 28 26 22 21 20 16.7 15.5

Example 3

A third sample spacer fluid (Spacer 3) was prepared and evaluated forfluid compatibility with a third oil-based mud (OBM3). Spacer 3 had adensity of 11.5 lbm/gal (1380 kg/m³) and composition provided in Table7. Spacer 3 was evaluated for fluid compatibility at 80° F. (27° C.) and180° F. (82° C.) with OBM3. OBM3 was a distillate-based invert emulsiondrilling mud. Spacer 3 and OBM3 were conditioned at the test temperaturefor 30 minutes prior to measurement. Ratios prescribed in API RP 10B2(2013) were prepared, and rheological measurements were taken on Spacer3, OBM3, and their mixtures using an OFITE 900 automated viscometerhaving an R1-B1-F1 configuration. Dial readings from the viscometer forthe fluids are shown at rotational speeds in Tables 8 and 9. Rotationalspeeds of 60 rpm and 100 rpm are of key interest as they most closelyapproach shear rates commonly experienced during primary cementing. At60 rpm and 100 rpm none of the mixtures experienced adverse gelation ora dial reading greater than 10% of that of Spacer 3, indicating goodfluid rheological compatibility for Spacer 3 and OBM3.

TABLE 7 Spacer 3 Composition Material Mass, grams Pumice 74.91 Diutan1.84 Barite 353.19 Solid Surfactant Composite 1 7.99 Solid SurfactantComposite 2 7.99 Fresh Water 656.48

TABLE 8 Rheological Compatibility of Spacer 3 and OBM3 at 80° F. Ratioof OBM3 to 300 Spacer 3 rpm 200 rpm 100 rpm 60 rpm 30 rpm 6 rpm 3 rpm100:0  12 9 5 4 4 1.4 1.2 95:75 12 8 5 3 2 0.7 0.6 75:25 14 10 7 5 3 0.60.4 50:50 32 24 15 10 6 3.2 3.0 25:75 34 29 22 18 12 5.3 4.1  5:95 38 3226 22 18 10.8 9.6  0:100 35 31 26 23 21 16.9 14.9

TABLE 9 Rheological Compatibility of Spacer 3 and OBM3 at 180° F. Ratioof OBM to Spacer 3 300 rpm 200 rpm 100 rpm 60 rpm 30 rpm 6 rpm 3 rpm100:0  8 6 4 3 3 1.0 0.9 95:75 8 6 3 3 1 1.0 0.9 75:25 9 7 3 2 1 0.9 0.950:50 29 22 15 11 7 4.9 4.8 25:75 21 27 23 19 14 8.7 8.1  5:95 33 30 2624 20 13.8 12.3  0:100 31 29 25 23 22 18.1 16.1

Example 4

A fourth sample spacer fluid (Spacer 4) was prepared and evaluated forfluid compatibility with a cement slurry (CMT) having compositionprovided in Table 11. Spacer 4 had a density of 11.5 lbm/gal (1380kg/m³) and composition provided in Table 10. Spacer 4 was evaluated forfluid compatibility at 80° F. (27° C.) and 180° F. (82° C.) with CMT.Spacer 4 and CMT were conditioned at the test temperature for 30 minutesprior to measurement. Ratios prescribed in API RP 10B2 (2013) wereprepared, and rheological measurements were taken on Spacer 4, CMT, andtheir mixtures using an OFITE 900 automated viscometer having anR1-B1-F1 configuration. Dial readings from the viscometer for the fluidsare shown at rotational speeds in Tables 12 and 13. Rotational speeds of60 rpm and 100 rpm are of key interest as they most closely approachshear rates commonly experienced during primary cementing. At 60 rpm and100 rpm none of the mixtures experienced adverse gelation or a dialreading greater than 10% of that of CMT, indicating good fluidrheological compatibility for Spacer 4 and CMT.

TABLE 10 Spacer 4 Composition Material Mass, grams Pumice 74.91 Diutan1.84 Barite 332.38 Solid Surfactant Composite 1 7.99 Solid SurfactantComposite 2 7.99 Fresh Water 677.29

TABLE 11 CMT Composition Material Mass, grams Type I/II Cement 440.47Type F Fly Ash 174.91 Elastomer 36.14 Silica Fume 21.61 Fluid Loss Agent1 3.07 Expansion Aid 24.62 Fresh Water 481.23

TABLE 12 Rheological Compatibility of Spacer 4 and CMT at 80° F. Ratioof CMT to Spacer 4 300 rpm 200 rpm 100 rpm 60 rpm 30 rpm 6 rpm 3 rpm100:0  138 105 66 48 31 11.5 8.3 95:75 146 110 71 51 34 13.2 9.7 75:25120 94 63 47 34 15.7 10.8 50:50 81 66 49 40 31 20.7 17.6 25:75 54 45 3632 27 21.3 19.4  5:95 40 34 28 26 23 19.0 16.4  0:100 35 30 25 23 2017.5 15.6

TABLE 13 Rheological Compatibility of Spacer 4 and CMT at 180° F. Ratioof CMT to Spacer 4 300 rpm 200 rpm 100 rpm 60 rpm 30 rpm 6 rpm 3 rpm100:0  82 63 40 30 19 6.8 4.5 95:75 86 67 44 33 22 8.0 5.5 75:25 75 6042 33 23 9.9 7.4 50:50 53 45 36 31 26 16.1 13.1 25:75 43 40 34 32 2924.2 21.9  5:95 34 30 27 26 23 19.2 17.2  0:100 29 27 25 23 21 18.5 17.0

It should be understood that the compositions and methods are describedin terms of “comprising,” “containing,” or “including” variouscomponents or steps, the compositions and methods can also “consistessentially of” or “consist of” the various components and steps.Moreover, the indefinite articles “a” or “an,” as used in the claims,are defined herein to mean one or more than one of the element that itintroduces.

For the sake of brevity, only certain ranges are explicitly disclosedherein. However, ranges from any lower limit may be combined with anyupper limit to recite a range not explicitly recited, as well as, rangesfrom any lower limit may be combined with any other lower limit torecite a range not explicitly recited, in the same way, ranges from anyupper limit may be combined with any other upper limit to recite a rangenot explicitly recited. Additionally, whenever a numerical range with alower limit and an upper limit is disclosed, any number and any includedrange falling within the range are specifically disclosed. Inparticular, every range of values (of the form, “from about a to aboutb,” or, equivalently, “from approximately a to b,” or, equivalently,“from approximately a-b”) disclosed herein is to be understood to setforth every number and range encompassed within the broader range ofvalues even if not explicitly recited. Thus, every point or individualvalue may serve as its own lower or upper limit combined with any otherpoint or individual value or any other lower or upper limit, to recite arange not explicitly recited.

Therefore, the present disclosure is well adapted to attain the ends andadvantages mentioned as well as those that are inherent therein. Theparticular embodiments disclosed above are illustrative only, as thepresent disclosure may be modified and practiced in different butequivalent manners apparent to those skilled in the art having thebenefit of the teachings herein. Although individual embodiments arediscussed, the disclosure covers all combinations of all thoseembodiments. Furthermore, no limitations are intended to the details ofconstruction or design herein shown, other than as described in theclaims below. Also, the terms in the claims have their plain, ordinarymeaning unless otherwise explicitly and clearly defined by the patentee.It is therefore evident that the particular illustrative embodimentsdisclosed above may be altered or modified and all such variations areconsidered within the scope and spirit of the present disclosure. Ifthere is any conflict in the usages of a word or term in thisspecification and one or more patent(s) or other documents that may beincorporated herein by reference, the definitions that are consistentwith this specification should be adopted.

What is claimed is:
 1. A method for displacing wellbore fluids,comprising: providing a spacer additive comprising: a biopolymercomprising diutan gum; and a scouring material selected from the groupconsisting of pumice, perlite, fumed silica, and combinations thereof,wherein the spacer additive comprises a dry blend of the biopolymer andthe scouring material, wherein the spacer dry blend has a diutan gum toscouring material weight ratio of about 2.4 to about 97.6, and whereinthe spacer dry blend is essentially free of crystalline silica,preparing a spacer fluid comprising by combining water and the spaceradditive, wherein the spacer fluid is essentially free of clay; andintroducing the spacer fluid into a wellbore to displace at least aportion of a first fluid in the wellbore.
 2. The method of claim 1,wherein the solid scouring material has a specific gravity of less than2.5, and wherein the spacer fluid is free of crystalline silica orcomprises crystalline silica in an amount of about 1 wt. % or less, notincluding any components having a specific gravity greater than 2.5. 3.The method of claim 1, wherein the solid scouring material has a Mohshardness of about 6 or greater, wherein the solid scouring material hasa roundness of about 0.6 or less, and wherein the solid scouringmaterial has a sphericity of about 0.6 or less.
 4. The method of claim1, wherein the biopolymer gum further comprises at least one gumselected from the group consisting of xanthan gum, welan gum,scleroglucan gum, and combinations thereof.
 5. The method of claim 1,wherein the solid scouring material comprises pumice, and wherein thebiopolymer gum comprises diutan gum.
 6. The method of claim 1, whereinthe spacer fluid further comprises a solid surfactant composite.
 7. Themethod of claim 6, wherein the solid surfactant composite has a meanparticle size of about 5 microns to about 1,500 microns, and wherein thesolid surfactant composite comprises a wetting surfactant on a solidcarrier.
 8. The method of claim 1, wherein the spacer fluid furthercomprises a defoaming agent.
 9. The method of claim 1, wherein the firstfluid comprises an oil-based drilling fluid.
 10. The method of claim 1,further comprising introducing a cement composition into the wellborebehind the spacer fluid.
 11. A method for displacing wellbore fluids,comprising: providing a spacer dry blend comprising a spacer additive, asolid surfactant composite, and a weighting agent having a specificgravity greater than 2.5, wherein the spacer additive comprises pumiceand diutan gum in a diutan gum to pumice weight ratio of about 2.4 toabout 97.6, and wherein the solid surfactant composite comprises asurfactant on a solid carrier; combining at least the spacer dry blendand water to form a spacer fluid, wherein the spacer fluid isessentially free of clay comprising montmorillonite clay, attapulgiteclay, and sepiolite clay; and introducing the spacer fluid into awellbore to displace at least a portion of an oil-based drilling fluidin the wellbore.
 12. The method of claim 11, further comprisingintroducing a cement composition into the wellbore behind the spacerfluid.
 13. The method of claim 11, wherein the solid surfactantcomposite has a mean particle size of about 5 microns to about 1,500microns, and wherein the solid surfactant composite comprises a wettingsurfactant on a solid carrier.
 14. The method of claim 11, wherein thespacer additive has a specific gravity of less than 2.5, and wherein thespacer fluid is free of crystalline silica or comprises crystallinesilica in an amount of about 1 wt. % or less, not including anycomponents having a specific gravity greater than 2.5.
 15. The method ofclaim 11, wherein the pumice has a Mohs hardness of about 6 or greater,wherein the pumice has a roundness of about 0.6 or less, and wherein thepumice has a sphericity of about 0.6 or less.
 16. The method of claim11, wherein the pumice has a mean particle size of about 1 micron toabout 200 microns.
 17. A method for displacing wellbore fluids,comprising: providing a spacer dry blend comprising: a biopolymercomprising diutan gum; a scouring agent comprising perlite; a solidsurfactant composite; and a weighting agent comprising calciumcarbonate, wherein the spacer dry blend has a scleroglucan gum toperlite weight ratio of about 2.4 to about 97.6; and combining at leastthe spacer dry blend and water to form a spacer fluid; introducing thespacer fluid into a wellbore to displace at least a portion of anoil-based drilling fluid in the wellbore.